Polycrystalline diamond (“PCD”) materials and PCD elements formed therefrom are well known in the art. Conventional PCD may be formed by subjecting diamond particles in the presence of a suitable solvent metal catalyst material to processing conditions of high pressure/high temperature (HPHT), where the solvent metal catalyst promotes desired intercrystalline diamond-to-diamond bonding between the particles, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making such PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. FIG. 1 illustrates a microstructure of conventionally formed PCD material 10 including a plurality of diamond grains 12 that are bonded to one another to form an intercrystalline diamond matrix first phase. The catalyst/binder material 14, e.g., cobalt, used to facilitate the diamond-to-diamond bonding that develops during the sintering process is dispersed within the interstitial regions formed between the diamond matrix first phase. The term “particle” refers to the powder employed prior to sintering a superabrasive material, while the term “grain” refers to discernable superabrasive regions subsequent to sintering, as known and as determined in the art.
The catalyst/binder material used to facilitate diamond-to-diamond bonding can be provided generally in two ways. The catalyst/binder can be provided in the form of a raw material powder that is pre-mixed with the diamond grains or grit prior to sintering. In other methods, the catalyst/binder can be provided by infiltration into the diamond material (during high temperature/high pressure processing) from an underlying substrate material that the final PCD material is to be bonded to. After the catalyst/binder material has facilitated the diamond-to-diamond bonding, the catalyst/binder material is generally distributed throughout the diamond matrix within interstitial regions formed between the bonded diamond grains. Particularly, as shown in FIG. 1, the binder material 14 is not continuous throughout the microstructure in the conventional PCD material 10. Rather, the microstructure of the conventional PCD material 10 may have a uniform distribution of binder among the PCD grains. Thus, crack propagation through conventional PCD material will often travel through the less ductile and brittle diamond grains, either transgranularly through diamond grain/binder interfaces 15, or intergranularly through the diamond grain/diamond grain interfaces 16.
Solvent catalyst materials may facilitate diamond intercrystalline bonding and bonding of PCD layers to each other and to an underlying substrate. Solvent catalyst materials used for forming conventional PCD include metals from Group VIII of the Periodic table, such as cobalt, iron, or nickel and/or mixtures or alloys thereof, with cobalt being the most common. Conventional PCD may include from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. However, while higher metal content increases the toughness of the resulting PCD material, higher metal content also decreases the PCD material hardness, thus limiting the flexibility of being able to provide PCD coatings having desired levels of both hardness and toughness. Additionally, when variables are selected to increase the hardness of the PCD material, brittleness also increases, thereby reducing the toughness of the PCD material.
PCD is commonly used in earthen drilling operations, for example in cutting elements used on various types of drill bits. Although PCD is extremely hard and wear resistant, PCD cutting elements may still fail during normal operation. Failure may occur in three common forms, namely wear, fatigue, and impact cracking. The wear mechanism occurs due to the relative sliding of the PCD relative to the earth formation, and its prominence as a failure mode is related to the abrasiveness of the formation, as well as other factors such as formation hardness or strength, and the amount of relative sliding involved during contact with the formation. Excessively high contact stresses and high temperatures, along with a very hostile downhole environment, also tend to cause severe wear to the diamond layer. The fatigue mechanism involves the progressive propagation of a surface crack, initiated on the PCD layer, into the material below the PCD layer until the crack length is sufficient for spalling or chipping. Lastly, the impact mechanism involves the sudden propagation of a surface crack or internal flaw initiated on the PCD layer, into the material below the PCD layer until the crack length is sufficient for spalling, chipping, or catastrophic failure of the cutting element.